Particles finer than 0.1 μm (10−7m) in water remain continuously in motion due to electrostatic charge (often negative) which causes them to repel each other. Once their electrostatic charge is neutralized by the use of a coagulant chemical, the finer particles start to collide and agglomerate (collect together) under the influence of
Van der Waals forces. These larger and heavier particles are called flocs. Flocculants, or flocculating agents (also known as flocking agents), are chemicals that promote flocculation by causing
colloids and other suspended particles in liquids to aggregate, forming a floc. Flocculants are used in water treatment processes to improve the sedimentation or filterability of small particles. For example, a flocculant may be used in
swimming pool or
drinking water filtration to aid removal of microscopic particles which would otherwise cause the
water to be
turbid (cloudy) and which would be difficult or impossible to remove by filtration alone. Many flocculants are multivalent
cations such as
aluminium,
iron,
calcium or
magnesium. These positively charged molecules interact with negatively charged particles and molecules to reduce the barriers to aggregation. In addition, many of these chemicals, under appropriate
pH and other conditions such as temperature and
salinity, react with water to form insoluble
hydroxides which, upon precipitating, link together to form long chains or meshes, physically trapping small particles into the larger floc. Long-chain polymer flocculants, such as modified
polyacrylamides, are manufactured and sold by flocculant producers. These can be supplied in dry or liquid form for use in the
flocculation process. The most common liquid polyacrylamide is supplied as an emulsion with 10-40% actives and the rest is a non-aqueous carrier fluid, surfactants and
latex. This form allows easy handling of viscous polymers at high concentrations. These emulsion polymers require "activation" — inversion of the emulsion so that the polymer's molecules form an aqueous solution. ==Agents==